1. Field of the Invention
The present invention relates to a method and apparatus for inserting an electronic watermark into digital data and a method and apparatus for detecting the electronic watermark from the digital data and in particular, to a method and apparatus for inserting an electronic watermark into digital video data and a method and apparatus for detecting the electronic watermark from the digital video data.
In addition, the present invention relates to a method and apparatus for encrypting digital data and a method and apparatus for decrypting the encrypted digital data and in particular, to a method and apparatus for encrypting digital video data and a method and apparatus for decrypting the encrypted digital video data.
2. Description of the Prior Art
In recent years, video data and audio data are digitized before being stored, transmitted, and distributed. Along with popularization of digitizing data, a problem that digital data are illegally copied arises. Technologies for inserting an electronic watermark into digital data and detecting the electronic watermark from the digital data are attracting attention as technologies for preventing the digital data from being illegally copied. Such technologies are being developed so that they can be commercially used. As a technology for preventing data and programs from being falsified, an encrypting system is known, beside the electronic watermark. In the encrypting system, data or a program is encrypted with a particular encryption key. Without the encryption key, the data or the program cannot be used.
However, such an encrypting technology has a drawback that once an encryption key is stolen, encrypted data can be easily decrypted. In the CSS (Contents Scrambling System) applied for a DVD (Digital Versatile disk), all the contents of DVDs are encrypted with an identical encryption key (a single encryption key or one set of encryption keys). Therefore, once the encryption key or the set of encryption keys is stolen, all the contents of the DVDs can be decrypted, whereby they can be illegally copied.
If each content is encrypted with a unique encryption key, the problem involved in the CSS can be solved. However, if respective encryption keys of contents of DVDs are supplied to a buyer of the contents in a different route from the route of the contents, the buyer has to set the respective encryption keys for each contents to a reproducing apparatus or a reproducing computer software. Thus, the buyer is obliged to perform a troublesome operation. Alternatively, if an encryption key is inserted into a particular area of MPEG (Moving Picture Experts Group) data, an illegal person can easily extract the encryption key from the MPEG data, decrypt the encrypted MPEG data with the extracted encryption key, and make a copy of the decrypted MPEG data.
JPA 11-317859 discloses a technology for inserting an electronic watermark into video data, scrambling the video data in block units while using the electronic watermark as a part of data for coordinate transformation in the scrambling the video data. In such a technology, the scrambled video data can be descrambled only when a reproduction side has the same electronic watermark as the electronic watermark inserted into the video data. However, in this technology, video data are not encrypted, though the video data is scrambled in block units. Thus, without need to descramble the scrambled video data, the electronic watermark can be detected from any frame. Consequently, in this technology, the electronic watermark cannot be concealed at all. In addition, since the video data have been scrambled in block units, there is no spatial continuity in the vide data. Thus, when the video data is to be compressed, a motion vector for each block cannot be detected. As a result, the motion-compensated inter-frame predictive encoding cannot be performed, whereby the video data cannot be highly efficiently compressed.